There is an increased emphasis on developing detectors with enhanced functionality at the pixel level. This can manifest itself as spectral, polarization, dynamic range or phase.
The important parameters of infrared detectors of course vary with application but include quantum efficiency (the fraction of incident photons contributing to the collection of an electrical signal), dark current (the current in the absence of an optical signal), and spectral bandwidth (the range of wavelengths over which the signal is received). Typical semiconductor photodetectors (InSb, HgCdTe, InAs/GaAs), quantum well infrared photodetectors (QWIPs), InAs/GaAs quantum dot infrared photodetectors (QDIPs), and InAs/GaSb strained layer superlattices have relatively broad spectral bandwidths of several micrometers or more. QWIPs and QDIPs typically have relatively low quantum efficiencies as a result of the low absorption cross section of an individual well or dot and limitations to stacking multiple wells or dots associated with the heterogeneous growth and the resulting strain limitations.
The exemplary embodiments herein enhance the quantum efficiency of QWIP and QDIP detectors by increasing coupling to the incident radiation field as a result of resonant coupling to surface plasma waves supported by the metal/semiconductor interface, without impacting the dark current of the device, resulting in an improved detectivity over the surface plasma wave spectral bandwidth. This concept is also applicable to SLS and bulk semiconductor devices by reducing a thickness of the active region, thereby reducing the quantum efficiency and the dark current, which is often proportional to the active volume, and regaining the quantum efficiency with the surface plasma wave coupling.
In some applications, spectral and polarization information is important. Today this is often accomplished with external optical elements (filters and polarizers) that add significantly to the cost, size, weight and power requirements (SWaP), and mechanical complexity of the infrared array implementation. As disclosed herein, the exemplary embodiments integrate the spectral and polarization selective elements directly on the detector array elements, thereby eliminating the added cost, SWaP and mechanical complexity.